b 1. Field of the Invention
The present invention relates to the field water purifiers and more specifically to an improved compound valve for controlling the operation of a reverse osmosis water purifying system.
2. Prior Art
U.S. Pat. No. 4,176,063 discloses a control valve for a reverse osmosis water purifying system that controls the operation of the system according to the water pressure present in the system's pure water delivery line. The control valve comprises four individual diaphragm valves linked together by hydaulic passages. The first of these diaphragm valves is a check valve inserted in the pure water delivery line that maintains pressure in the line between the check valve and the spigot when the spigot is closed. The second diaphragm valve is a pilot valve hydraulically linked to the pure water delivery line such that the pilot valve opens when the pure water pressure is low, i.e. when the spigot is open. The third diaphragm valve is a squeeze water valve which opens in response to opening of the pilot valve and controls the flow of pressurized waste water from the reverse osmosis unit to a pure water tank in which the pure water is maintained in a bladder. The pressurized waste water is used to pressurize the pure water to provide adequate pure water delivery pressure when the spigot is open. Finally, the fourth diaphragm valve is an inlet water valve which controls the inflow of water from the main water line to the system. This inlet valve is closed only when the pure water tank is completely filled with pure water.
This prior art control valve has subsequently been improved by the addition of two additional valves. The first of these, a duck bill valve, assures that there is always a limited flow of waste water through the reverse osmosis unit to remove salts and other impurities from the unit's filter membrane whenever water is being filtered. The second, a diverter valve, allows squeeze water from the pure water tank to flow to a drain to eliminate the back pressure in the pure water tank during the filtering process.
Two major problems remain with the operation of the improved prior art valve. The first arises when a long pure water delivery line is used between the valve and spigot or when the system is used to deliver pure water to an automatic ice cube maker. Under these circumstances, when the spigot is opened or the ice cube maker valve is turned on there is initial drop in pressure in the pure water deliver line causing the pilot valve and the squeeze valve to open. However, because of the resistance of the long delivery line or the typically small water valve in the ice cube maker, after this initial drop in water pressure the water pressure in the pure water delivery line rises a certain degree. This pressure causes the pilot valve and squeeze valve to shut shortly after they have been opened. Once the squeeze valve has shut, the pure water pressure drops, and the pilot and squeeze valves once again open. The cycle is repeated, resulting in oscillations in the flow of water and an unpleasant thumping noise in the valve that is transmitted along all the pipes of the system.
A second problem exhibited by the improved prior art valve is leakage of waste water to the drain when the squeeze and pilot valves are open, causing a reduction in the available pure water delivery pressure.